I believe I have that same switch on my boat. Two large 12 volt batteries with the negatives connected to a common rail and a Perko that allows Off/batt1/batt2/both. Is that what you have?
Yes, the trickle charger will charge both when the switch is on "both". Both batteries will interact with the charger OK, but you have to think what else might happen because the batteries can also interact with each other. Best to read on a bit farther before doing much of that.
There's an odd problem that can happen when the Perko switch is set to "both" unless steps have been taken to limit how the batteries interact with each other.
All the Perko switch does is the simplest thing possible - it hooks the like terminals of both batteries together (usually the +), and depending how the rest of the boat is wired there's a possible problem when the like terminals of two batteries with different charges are hooked together. Of course the problem only happens if the other terminals (the - in this case) of both of those batteries are also hooked together into a common rail or common floating ground - but that is usually how most boats are wired and chances are yours is too.
So suppose the batteries are both hooked up that common way and you have been using battery number one to power reading lights last night and sort of saving battery number two...just like I often do and the result is that now one battery is at a lower charge (and also a lower voltage than the other).
And now you want to switch the Perko onto "both" because you want to charge both at the same time....but you wonder if this is a good idea. Is that right?
Assuming the common rail system, switching the Perko to "both" will put those two batteries into parallel. Now the battery with the most charge - which will also have the higher voltage - will promptly attempt to charge the other battery. If the voltages aren't all that different then not much will happen, but make sure that both your wiring between the batteries and the Perko switch itself is up to handling that many potential amps without overheating.
I do this and haven't had a problem yet, but first I check the battery voltages and don't do it if the voltages are much different. What I'll do instead is switch over to the higher battery and drain it down a bit first.
Still, that "both" setting is tempting and would be useful for equalizing batteries as well as charging them from a single source. And there is one other thing that you can do and that is to add a few items to the circuit to limit the interaction of batteries when they are put in parallel. That's the best of all worlds and it's the tack I'd recommend - although I admit I haven't done it in my own boat....
With a little thought it ought to be possible to limit the interaction of multiple batteries with some diodes and possibly some resistors so that I could use the "both" feature without concern. Or maybe there is a commercial unit that someone can recommend...? I've been meaning to do this but haven't yet.
Roger L.
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From: dsailormonSent: Monday, August 19, 2013 6:57 AMSubject: [Electric Boats] perkos switch and battery chargeri am not an electrical person. i did install a thoosa on my 30 ft alberg. but i have another boat with a two battery setup and a perko switch. the question for all u electrical folk----if i have a trickle charger on one battery and the perko switch on both will both batteries be charged. probably a simple question for ya'll but would appreciate knowing. thanks in advance
dan
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